As kids explored our equipment, parents talked about allowing their children to sleep in their car seats.

"I try to keep him asleep as much as I can and tiptoe the car seat out of the car and into the house or into the store," confessed Cortney Hawkins.

Jennifer Wilson does it too.

"'Cause it was always easier that way than waking her up and carrying her with me while I would shop."

But researchers in Michigan are now cautioning parents to stop the practice, after finding cancer-causing chemicals in some seats, and in others chemicals whose effects aren't even known.

"Many of these are hormone disrupters and the impact of these can be significant," according to Jeff Gearhart of The Ecology Center, where they have tested chemicals in car seats

We visited Gearhart and his colleagues in Ann Arbor just days before releasing their latest report on car seats.

The non-profit environmental organization began testing seats ten years ago.

"It's a safety device," he said. "If you are transporting a child in a car you have to purchase one. You don't have an option to say I am not going to buy one because I am concerned about exposure."

But the organization does want to track what chemicals are used in the seats, and offer ratings.

So why are there chemicals present at all?

It all goes back to the 1960s, when more people smoked and car upholstery began to be treated with flame retardants, should ashes ignite the fabric.

Car seats were added to the federal flammability standard for vehicles in 1981.

The problem was no specific chemicals were ever given to use or not to use.

And now these chemicals, many of them phased out of clothing and furniture, are still showing up in car seats.

Even worse, manufacturers themselves may not know exactly what chemicals are being used.

"So sometimes even when they try to find out what their supplier is using it's difficult. And they can tell their supplier 'okay here are our rules'. But then (manufacturers) need to check up on it," said Gillian Miller, a scientist at The Ecology Center.

That happens here at the labs of the Ecology Center.

In 2016, they tested 15 popular seats ranging in price from $50 to $400.

And for the first time they found a seat, the UPPAbaby Mesa Henry, free of any flame retardants.

Its cover is made of a wool blend that is naturally flame retardant.

However, it is more expensive and the flame retardant-free car seat does not go on sale until Spring 2017.

As for the rest, the Ecology Center grouped them by toxicity, giving top marks to Britax and Maxi-Cosi models.

But several other popular brands, which did well in crash tests, did not fare as well when it comes to chemicals.

So what can parents do?

As mentioned, limit their use. That means use them for travel only not for napping.

Also, keep the seats clean. Chemicals can flake off fabrics and find their way into nasal passages and mouths.

"They tend to stick to dust, and dust gets accidentally ingested or it can get into the air," Miller said.

Also wash your child's hands once out of the seat.

A federal bill introduced last spring would allow car seats to be made without these chemicals. Lawmakers have the ability to mandate a change.

NOTE: Properly installed car seats in cars save lives. The safest place for a child in a vehicle is in a rear-facing car seat, in the middle of the back seat. No information within this story should be interpreted to imply otherwise.